diff --git a/modules/brep/io/brepIO.ts b/modules/brep/io/brepIO.ts
index 99fe1646..dfc05dde 100644
--- a/modules/brep/io/brepIO.ts
+++ b/modules/brep/io/brepIO.ts
@@ -114,7 +114,7 @@ function readSurface(s, faceInverted, effectivelyInverted, face) {
     surface._mirrored = !s.direct;
   } else if (s.TYPE === 'PLANE') {
     
-    let normal = new Vector().set3(s.normal);
+    let normal = new Vector().set3(s.normal).asUnitVector();
     let plane = new Plane(normal, normal.dot(new Vector().set3(s.origin)));
     if (effectivelyInverted) {
       plane = plane.invert();
diff --git a/modules/geom/surfaces/brepSurface.ts b/modules/geom/surfaces/brepSurface.ts
index 559b1ed4..e23c22e7 100644
--- a/modules/geom/surfaces/brepSurface.ts
+++ b/modules/geom/surfaces/brepSurface.ts
@@ -1,5 +1,5 @@
 import {Point} from '../point';
-import Vector from 'math/vector';
+import Vector, {UnitVector} from 'math/vector';
 import {Plane} from '../impl/plane';
 import BrepCurve from '../curves/brepCurve';
 import {intersectNurbs} from './nurbsSurface';
@@ -55,13 +55,12 @@ export class BrepSurface {
     return normal;
   }
 
-  normalUV(u: number, v: number): Vector {
+  normalUV(u: number, v: number): UnitVector {
     let normal = pt(this.impl.normal(u, v));
     if (this.inverted) {
       normal._negate();
     }
-    normal._normalize();
-    return normal;
+    return normal._normalize();
   }
 
   normalInMiddle(): Vector {
diff --git a/modules/math/vector.ts b/modules/math/vector.ts
index 830634e5..0dfed654 100644
--- a/modules/math/vector.ts
+++ b/modules/math/vector.ts
@@ -1,5 +1,6 @@
 import {clamp} from "math/commons";
 import {XYZ} from "math/xyz";
+import {areEqual, TOLERANCE_SQ} from "math/equality";
 
 export default class Vector implements XYZ {
 
@@ -182,7 +183,14 @@ export default class Vector implements XYZ {
     const sinA = clamp(this.cross(vecB).length(), -1, 1);
     return Math.atan2(sinA, cosA);
   }
-  
+
+  asUnitVector(): UnitVector {
+    if (areEqual(this.lengthSquared(), 1, TOLERANCE_SQ)) {
+      console.error("not unit vector is treated as unit");
+    }
+    return this as any as UnitVector;
+  }
+
   static fromData(arr: [number, number, number]): Vector {
     return new Vector().set3(arr);
   }